| Popis: |
Photorefractive polymer materials offer a number of potential advantages over inorganic materials, particularly low cost of material, low dc dielectric constant, ease of fabrication, and compatibility with integrated optics. Our first reports of photorefractivity in an organic polymer1 established the presence of the effect by a combination of hologram erasability, correlation with photoconductivity and electro-optic response, and enhancement by external fields in numerous samples (≃350 μm thick) of the epoxy polymers bisA-NPDA (bisphenol-A-diglycidylether-nitrophenylenediamine) or NA-APNA (N,N-(diglycidyl)-4-nitroaniline-N-(2-aminophenyl)-4-nitroaniline) mixed with three different hole transport agents similar in structure to p-diethylaminobenzaldehyde-diphenyl hydrazone (DEH). Diffraction efficiencies up to 0.1% (NA-APNA) and 0.06% (bisA-NPDA) were observed at bias fields of 84 kV/cm and 126 kV/cm, respectively. Using standard Kukhtarev theory to model the field dependence of the results, we find bestfit values for the space-charge field in the bisA-NPDA/DEH mixture of 26 kV/cm at an applied field of 126 kV/cm and a grating spacing of 1.6 μm; the estimated photorefractive trap density was 1.9 × 1015 cm-3. The steady-state diffraction efficiencies show a polarization anisotropy in agreement with the photorefractive interpretation. Recent experiments to fully characterize the photoconductivity and to extend this work to other materials systems are summarized. |
